Engine Rebuild

4.0 Head / 4.2 Block

Sooner or later, every CJ owner will need to ponder the fate of their engine.  That time came for me not too long ago.  I had been very pleased with my straight six engine when it came to its power and low-end torque.  Also, since having converted the fuel intake over to the Mopar Multi-Port Injection system, I was rather committed to staying with the inline six engine when it became time.  When my rings finally gave out, I had three options for my next engine:

Option 1 - I could pull my 4.2 engine out and have the whole thing rebuilt.  This would have been the least expensive option as I already had all of the parts.  But I was hesitant because with my MPI fuel injection I was getting some occasional pinging problems.  This would be a good opportunity to resolve this problem and help the engine breathe better.  

Option 2 - I could find a new (remanufactured) 4.0 engine and implant it into my CJ.  With this option, I could still use my existing engine mounts, bellhousing, and clutch, as the AMC six-cylinder motors all share the same bolt pattern at the bellhousing.  Also, if you have the Mopar MPI fuel injection conversion, all these parts apparently will work on the 4.0 engine.  This seems obvious because the MPI kit is based on a 1994-95 4.0 engine, but I wasn't sure how many of the kit parts were "customized" to work only with the 4.2 engine.  I also wasn't so sure how many other parts, like the power steering pump or alternator brackets, would work with the different 4.0 engine.  One big drawback of this route is that most places require a "core charge" when you buy a new engine, and the old 4.2 block will not work in lieu of this charge.  This could add another $600 to the price of this option.  The 4.0 engine (with the fuel injection) is, however, much stronger than the 4.2 in the above option.

Option 3 - This option is the hybrid of the two previous options, mating a 4.0 head on top of the 4.2 block.  In this option, I would have to rebuild the short block of my 4.2 and then get a 4.0 head (with some modifications) to fit on top of the 258.  I have seen a number of websites mentioning this conversion, and heard a number of good things about it.  You still have the expense of rebuilding the old engine (less the head), and you have the expense of finding a new 4.0 head.  Rumor has it the hybrid engine is even more powerful than the 4.0 engine (with the fuel injection) mostly in the torque produced.

It sounded relatively simple...

Will that be cash or charge?

As the title of this project page shows, I went for Option 3.  There is no getting around the fact that it can be pretty expensive to rebuild your engine.  Even doing a lot of the work yourself, the task is not cheap.  In the end, I learned that doing the work myself didn't necessarily save me a ton of money (although it did save me some) but more importantly it let me know that everything in the engine was new and it was installed properly.

As I mentioned above, I already had converted my fuel intake over to the Mopar MPI fuel injection and have been very happy with the resulting engine performance from that upgrade.  However, I knew when I installed the fuel injection that my engine wasn't going to last forever.  Eventually it lost several compression rings and needed to be rebuilt.  I wanted a better set-up for the engine and eventually opted for Hesco's 4.2L to 4.0 Head Conversion kit specifically for the 258 engine.  Hesco is the company that puts together the MPI conversion kits.  They have been very helpful with their knowledge on the subject of fuel flow into the Jeep motors and I felt comfortable with their reputation.

Their head conversion kit comes with a remanufactured head with new valves and springs, and has already been modified with the appropriate water jackets plugged specifically for the 4.2 L (258 c.i.d.) engine.  They sell this kit as a complete bolt-on unit.  I think "almost complete" would be a more appropriate description for the kit.  The kit includes a new metal valve cover (without a gasket), the hardware for the valve cover, two studs for the exhaust manifold ends, two dowel pins (for the intake manifold), a 4.0 head gasket, and an intake manifold gasket.  Rocker arms are not included with the kit.  It is very likely your old rocker arms will be too worn-out to reuse.  Perhaps Hesco's reasoning for not having rocker arms is that there are a variety of rocker arms you can choose from and they let you decide which ones to go with?  But it would be nice when making a budget to know that rocker arms are not included.  So now you know.

The new 4.0 head will require a new exhaust manifold.  Your 4.2 exhaust manifold or header will not work.  (So much for my old Borla header!)  I was impressed with the Borla header I had (and my Borla Cat-Back system), so I opted to get a new 4.0 header.  One thing to note for the CJ owners in this situation, the new 4.0 exhaust system was designed for the YJ vehicles with the final exhaust exiting the vehicle on the passenger side.  So some simple modifications will be necessary to link the end of the header to the existing catalytic converter location.  The Borla 4.0 header I got was for the 1991-92 YJs. 

What to expect...

The following steps document how I went about this project.  In the sidebars, you can read about what I learned/discovered along the way, and where I made some wrongful assumptions.  The following is NOT intended to be a "this is the way it must be done" procedure, but rather "this is what you might expect."  If done properly, the result should be very satisfying.


Engine Removal

Step 1 The first step before pulling the engine is to have a plan.  Take a few minutes and look carefully at what you think might need to be out of the way before the engine can be pulled out of the frame.  Don't forget your physical space either (height of your work space or room in front of the Jeep to move the engine hoist).  Under the hood, decide what components need to be removed and what can stay in place.
remove front components.jpg (57678 bytes) Then start with the more obvious: radiator (drain and contain coolant properly), fan, radiator shroud, hoses, belts, engine oil, battery, air cleaner, manifolds, starter motor, plug wires and distributor.

For those of you with the Mopar MPI, here's a hint!  After the plugs are out, rotate the crank around to Top Dead Center for the number one cylinder.  Remove the distributor cap and check that the rotor is pointing in the Number 1 position (should be toward you if you're standing on the side looking in).  Then pull the rotor and the plastic cover below the rotor (with the wire attached to it).  You should see a white piece of plastic with about three holes in it.  Under one of those holes will be a hole drilled in the bottom of the distributor.  Take a long thin bolt (or nail) and place it through the white plastic piece and through the hole on the bottom of the distributor.  You have now indexed the distributor and you can pull it from the block.

Step 3 By now you should have discovered the need for masking tape and a felt pen.  Find a safe area to carefully sort and store all the hardware from the removed parts.  While many of the nuts and bolts will be the same wrench size, their length and washer configuration will vary greatly.  You will thank yourself in about two weeks when you get around to tracking down all these parts again!
Step 4 Finally, for those parts that don't need to be extracted from the engine bay (e.g., wiring harness, power steering pump) make sure they are securely out of the way.  Using zip ties comes in handy for holding them out of the way, too.
Step 5 Now you can unbolt the engine mounts and start hunting for those seven bolts that hold the block to the bellhousing.  Swivels, extensions, spare hands, universal socket fittings, these are all handy to have at getting to the upper bolts on the bellhousing.  Don't forget the flywheel access cover plate near the bottom (you'll have to remove part of the clutch bellcrank linkage for this)!
lifting motor out.jpg (55566 bytes) Once you're this far, you can start to hunt for good places to attach your chain for the hoist.  Don't try to balance the engine side by side.  Find one near the front on one side, and one near the back on the other side.  Doing this, you can set the hook on a specific chain link to achieve the proper balance you need - or correct it if you need a specific angle.  Now you can start to lift AND pull.  Remember, the back of the engine (flywheel and clutch) will be held by the transmission's input shaft, so work the engine forward as you lift.  You may have to go up and down a few times to get it to separate.
airing down 3 more inches.jpg (49946 bytes) After the flywheel/clutch are free from the transmission input shaft, you can ease the engine out.  If you look carefully at this photo, you'll see how we dealt with needing to lift the engine out of a lifted Jeep!  The hoist will only lift so much.  If you need a few more inches, pull your valve cores out of your front tires!  (You can lower the front about 4 more inches.)
motor on pallet2.jpg (44070 bytes) We used an old pallet to set the engine down on after removing it from the Jeep.  At this point remove: the clutch, the flywheel, the harmonic balancer (using a special puller), the water pump, the thermostat housing, the alternator and its brackets, the timing chain cover, the valve cover, and the oil pan bolts.  I left the oil pan on the engine after I removed the bolts (but take the drain plug off).  I did this so the oil pan would get cleaned at the machine shop along with the engine.
pistons 1-4.jpg (50006 bytes) Next, the cylinder head assembly can be removed.  Be sure to carefully keep your push rods from getting bent in case you plan to reuse them.  This is where it gets fun!  Here, you can finally get a peek at what may have been going on inside that old engine.
Step 10 If you can, try to carefully remove your dip stick tube from the block.  You may have to help it from the bottom side (by removing the oil pan).  These are easy to break and Jeep is very proud of them.  A new one will cost you about $80 so take your time...
Step 11 You should now have what is referred to as a "short block."  It is "short" in that the engine does not have the head or most of the "tin" attached to the block.  The stripped-down engine can now be taken to the machine shop.

At The Shop (Part 1)

This is the first CROSSROAD you come to and you will need to make a few choices!  At this point, you need to decide on what you will be willing to do to your engine, or if you may even want to go much further with your engine (in the event the engine has been at this crossroad once before).

The first step at the shop is to get an estimate for all the labor in the machine shop.  This list will probably include the following: 

bullet Degrease the block
bullet Surface the block - I had 0.010" taken off the deck.
bullet Bore the cylinders - They were bored 0.030" over.
bullet Line bore the block
bullet Balance the engine - you will need to provide both the flywheel and harmonic balancer for this option.
bullet Insert cam bearings
bullet Insert plugs
bullet Resurface the flywheel
bullet Recondition the connecting rods
bullet Press the new pistons
bullet Machine 1/2" head bolts into the block - this is necessary if your 258 block has the 7/16" head bolts as the 4.0 heads require 1/2" head bolts.
bullet Reassemble (short block)

You will also need to get an estimate for the new parts at this point.  Since the piston size won't be known until after the block is checked and bored, all of the parts cannot be ordered at this time.  Most often you will opt for a Master Rebuild Kit that includes the pistons, rings, gasket kit, cam, timing chain set, oil pump (but no screen), lifters, bearings, and plugs.

In addition to the obvious parts, I also opted/needed to have several other parts replaced at this time.  You can always rebuild a engine on a tighter budget, but if you plan to keep the Jeep/engine for a while, it is better to replace anything you don't want to have to work too hard to replace later!  You may want to keep this fact in mind if you're buying a used vehicle with a "freshly rebuilt" engine.  How many old parts were reused?

New Parts

complete gasket kit.jpg (35140 bytes) Complete gasket kit (this comes with the Master Rebuild Kit).  All of the gaskets are included - and maybe a few extras.  So don't be too surprised if there are a couple left over.
new oil pump-screen.jpg (47140 bytes) New oil pump and screen.  Be careful about opting for a high-pressure oil pump as they can be harder on the seals.  Rather, a high-volume oil pump may be more desirable.  I stuck with the stock pump as I have always had good oil pressure in my engine.
new rocker arms.jpg (42230 bytes) As was mentioned above, the "complete" 4.0 Head Conversion kit from Hesco does not come with new rocker arms.  I opted for the stock rocker arms for now.
new lifters.jpg (46054 bytes) New hydraulic lifters.  These are what sit on top of your cam buried down inside the block.  The push rods fit into the tops (seen here) and push up against the bottom end of the rocker arms.
Centerforce boxes.jpg (47459 bytes) Since the old engine dumped a bunch of oil out the back, the bellhousing had quite a bit of oil inside.  The oil is very hard on your clutch, and in my case ruined the clutch.  I had my clutch replaced about two years ago and it was almost shot.  This time, I decided to try the Centerforce 1 clutch.
throw-out bearing.jpg (39984 bytes) While you're at it, get a new pilot bushing and throw-out bearing for that new clutch!  And don't forget to get a clutch alignment tool, too!
new-hoses-w-pump.jpg (40899 bytes) I also got a new water pump and some hoses.  I didn't really need a new water pump, but since everything else in the engine was new and I didn't want to have problems with my investment... well, it just made sense!

Cleaning and Making Repairs...

dirty engine bay.jpg (48595 bytes) Since the engine will be in the shop for a while this will be the opportunity to get yourself inside the engine bay and start cleaning!  Of course, remember to be careful with the wiring and those loose parts.
dirty bellhousing.jpg (51848 bytes) Here you can see the dirty bellhousing I mentioned above.  With the down-time, this is when you can clean up... 
cleaning-bellhousing.jpg (37283 bytes) Compressed air, chemicals, rags, and elbow grease!

With everything getting cleaner under the hood, and with no engine in the way, this is a good time to tackle some other necessary repairs.  I replaced my brake proportioning valve while I had easier access to all the brake lines.  It still was a pain...

At The Shop (Part 2)

I got lucky for a change when I learned that my engine did not require an alignment bore.  This saved me $150 - or paid for the engine balancing, depending on how you look at it.  I did learn that the shop, after drilling and tapping the 1/2" holes for the head, checked all the threaded holes on the block.  They found two holes that needed to be heli-coiled.  That added a whole $22 to the price!

I also had to get a few more new parts.  The ring gear on the flywheel was worn, so that had to be replaced as did my cover for the timing chain.   The shop repaired my broken dipstick tube, so that saved me a lot of hassles.  Since the new valve cover didn't come with a gasket (the manual says to use silicon) I bought a cork gasket for the cover.  The cork is less messy and easier to deal with.  Finally, I got a new set of spark plugs.

undrilled temp sending unit.jpg (38666 bytes) While inspecting the 4.0 head I got from Hesco, I discovered that there wasn't a tapped hole on the back edge for the temperature sending unit.  I took the head and the sending unit to the machine shop and had them drill and tap the hole so I could use my stock temperature gauge on my CJ.  It turned out to be an easy fix.

  After a little over a week, the rebuilt block was ready!

Reassembling the Engine
wraped block on stand.jpg (46300 bytes) The new engine came home with the crank and cam installed, and the new timing chain in place.  The engine was clean and wrapped in plastic!
clean-oil-pan.jpg (41375 bytes) After unwrapping the plastic, the oil pan was removed.  As mentioned above in Step 8, I left the oil pan on the short block so I could have it cleaned (both inside and out).
new-crank-cam.jpg (45056 bytes) Here's a look at the newly assembled crank and cam.  Note the use of the engine assembly lubricant on the cam lobes.  This helps lubricate the new engine before the oil has had a chance to circulate through the engine.
taped-to-paint.jpg (43252 bytes) It is a good idea to paint your engine.  For one, it makes it look nicer.  But the best reason is that it can help you spot oil leaks and other problems early on.  Before painting, carefully tape over anything you don't want paint on, or in.  Here, I used my old timing chain cover to protect the new chain and gears.
painted-red-block.jpg (46620 bytes) Once everything is covered, have at it.  Again, be very careful about getting paint in places you don't need to have painted.  The cast iron block will really absorb a lot of the paint.  Plan on several light coats.
painted-parts-black.jpg (53671 bytes) While the block is drying, you can paint the other items that will be bolted on later.
installing-oilpump-screen.jpg (25816 bytes) Once everything is painted, the engine should be ready to be fully assembled.  We started with putting the new screen on the new oil pump.  This ended up being harder than it would seem so we used a bench vise to help hold the pump while the screen's tube was slipped into the hole.
installing-oilpan.jpg (39119 bytes) With the oil pump and screen bolted to the bottom side of the block, the oil pan could be bolted back on.  I got a new one-piece oil pan gasket that made life really easy.  The oil pan gaskets in the master gasket kit are four separate pieces, and some have six!  The one piece gasket will be much easier to deal with when the engine is in the vehicle (if you ever need to later remove the oil pan).  Of course, working on an engine stand makes the job that much easier! 
installing-lifters.jpg (40649 bytes) With the oil pan bolted down, the engine can now be flipped over.  The next step is to install the new lifters.  Here my dad is coating the lifters (bottom and sides only) with engine assembly lube.  The 12 lifters are then dropped down into their holes above the cam.
Step 10 Once the lifters are in place, the deck surface needs to be thoroughly cleaned.  Make sure all the tape is removed (if you painted it) and that nothing has fallen into the engine.  Compressed air will remove the big pieces.  Then clean the surface with brake cleaner to remove any signs of oil.
Step 11 A 4.0 head gasket is used with the 4.0 head on the 4.2 block!  The Hesco kit included a new head gasket as well as new 1/2" head bolts.  The head gasket and head were then placed on top of the block and the new bolts were inserted into the block.  
threadsealant-on-11.jpg (31405 bytes) The head bolts tightening sequence numbers each of the bolt - starting with the two in the center and rotating outwards in a concentric circle.  There are two special notes for the Number 11 bolt as this one goes through the thinnest part of the head near the thermostat hole up front.  The first note deals with using a thread sealant.  This bolt will be in the water jacket and thus the sealant is used to keep the coolant from leaking past this bolt.  The manuals recommend Loctite 592 for this.
Step 13 The second note deals with the torque sequencing.  Now that you have 1/2" head bolts, the torque specification is much greater for these bolts.  Start by tightening all bolts to 22 ft/lbs following the circular torque sequence.  Then tighten all the bolts to 45 ft/lbs following the same sequence.  Recheck all bolts at 45 ft/lbs (same sequence).  Then finally tighten all bolts (EXCEPT #11) to 110 ft/lbs in the same sequence.  Bolt Number 11 should only be tightened to 100 ft/lbs so as to not risk breaking or damaging the head in this thin area.
installing-pushrods.jpg (48558 bytes) Once the head is in place, the push rods are next.  These just drop down onto the tops of the lifters.

In theory, the 4.0 head conversion is suppose to use the stock 4.2 sized lifters and push rods.  My stock push rods were fine (I checked them for wear on the ends and for straightness).  Read further as a problem later developed with my engine...

installing-rocker-arms.jpg (42359 bytes) Next, the new rocker arms and bridges can be placed on the head.  Make sure the push rods are still centered on top of the lifters (they should be able to depress some on the lifter's springs).
torque-rockers.jpg (44938 bytes) Now the rocker arms can be tightened down.  Be careful not to just tighten one side down.  The little bridge (linking each to the pairs of rockers) can get damaged if one side is tighten fully before the other side.  Tighten about a 1/2 turn each side, back and forth until they are both at 19 ft/lbs of torque.
Step 17

Problem Check!

While the rockers are non-adjustable (since they're hydraulic) it is easy to assume everything is fine.  But before going any further, make sure the rockers are not holding the valves open!  I regrettably didn't do this.

When each cylinder is at Top Dead Center, the valves should be fully closed.  When the valves are closed, you should be able to depress the back side of the rocker arm (above the push rod) and get a slight movement of the rocker.  In my case, the push rods were essentially too long, and the valve stems were being depressed at TDC!  This will result in no compression on the engine when you try to start it.  Make sure you check this now!

installed-waterpump.jpg (48020 bytes) Now you can bolt on the water pump, thermostat housing, timing chain cover, and engine mount brackets.
checking for fit.jpg (43814 bytes) With the engine on the engine stand and free access to all sides, this is the best opportunity to check they everything is going to fit properly.  I started with the intake manifold and the new 4.0 headers.  I discovered a small tab on the headers (near the lower center mounting hole) was too wide and it made getting the manifold bolt in impossible.  It was much easier to mark and measure what needed to be adjusted (grinded) at this point!

Also, make a note to check that the shoulders on the manifold bolts are wide enough to reach both the headers AND the intake manifold.  As the 4.0 intake manifold will sit higher above the exhaust manifold, your old washers may not be wide enough.

Step 20 If you go the route of a Borla header, you may find that your power steering back bracket (the one that mounts to the lower block) is going to interfere with the number one exhaust pipe.  Head over to the bench grinder!

If you already modified your bracket after installing the Mopar MPI intake manifold, you still have to cut some more material off the bracket.  I ended up cutting past the welded nut on the back side of the bracket.

PS-bracket-mod-clearance.jpg (42406 bytes) This photo shows the tight fit of the modified bracket AFTER I finally got it to work.  There is about 3 mm of clearance between the header pipe and the bracket.  Click here for an even closer view!
PS-mod-lower-holes.jpg (34095 bytes) After removing the welded nut from the rear bracket's back side, I measured the distance between the fixed-point mounting hole on the bracket (for the power steering pump) and the hole I had removed the nut from (for the adjustable long-bolt allowing the pump to pivot).  Using that measurement, I set my calipers and scribed an arch from the fixed point hole through the old hole and down.  I found that approximately 0.75" below the center of the old hole, was enough to allow a bolt to clear the header pipe.  I then scribed a similar hole on the front mounting plate and drilled two new holes.

In this picture, you can see the end of the bolt coming through the new lower hole (it has the nut on it). 

check-fit-alternator-ps.jpg (46012 bytes) With the power steering pump mounted and out of the way, you can then mount the alternator and idle pulley wheels to check for proper belt alignment.  You will need to install your harmonic balancer to finish checking this!
Step 24 After everything fits and has been adjusted, you can remove the manifold and headers to keep them safely out of the way.  (I took this opportunity to install a new Adjustable Fuel Pressure Regulator on the intake manifold while it was easily accessible on the engine stand.)  
Step 25 Now you will need to take the engine off of the engine stand.  Attach the engine to the hoist the same way as was done in Step 6.
Install-clutch-OOPS.jpg (38400 bytes) BEFORE you attach your flywheel and clutch, don't forget to reattach the backing plate!  This picture shows that we got a little too anxious.

But while I have this photo up, the flywheel is attached to the back of the crank.  There should be 110 ft/lbs of torque for these bolts.  Next comes the clutch disk and housing.  Don't forget to use the clutch alignment tool while checking it as you tighten the housing to the flywheel.  Make sure the tool can be removed freely as the clutch is tightened. 

Step 27 Now the clutch throw-out bearing can be replaced.  I changed the rubber dust boot, too.  Double check everything!  Make sure there is nothing in the way in the engine bay.
Lowering-in-motor.jpg (48268 bytes) Carefully guide the engine back over the grill and into the engine bay.  This is the time to pull the clutch alignment tool out.  The trick here is to have someone under the vehicle to guide the transmission input shaft through the clutch while lifting the bellhousing up to accommodate the angles of the engine as it is being set in place.
Motor-set-in-place.jpg (60265 bytes) Once the bellhousing has fully seated to the back of the block, the engine can be bolted to the engine mounts and the bellhousing bolts can be attached.  You can't see him, but my friend Chad is down there doing that as I was taking the pictures!
Finished-almost.jpg (54342 bytes) From here on out the job is just attaching all the components back onto the engine.  A couple reminders: 

Don't install the dipstick tube back into the block until after the engine is and set.  This will greatly reduce your changes of breaking it off at the base, where it enters the block.

When you reinstall the distributor, make sure the engine is back at TDC on the compression stroke (exhaust valve should be closed).  Once this is in place, you can put the distributor back in and remove the long thin bolt you set in Step 2.

Step 31 Take a few minutes to double-check everything is in place and tight.
Step 32 Fluids.  Fill the engine with oil.  Fill the power steering pump with fluid.  Fill the radiator (check the overflow bottle).  Clean the air filter.
Step 33 See if it works!


Be very careful about re-using your old hoses.  If your old engine blew oil everywhere and oil got on your hoses, the oil can break-down the rubber and make the hoses soft.  For the price of the new engine, don't kill it by neglecting to replace a $6 hose.

When you first start your engine (and you are confident it will run for a while), don't let it just sit there and idle!  Run the engine up to 2000 RPMs for about 20 minutes before leaving the garage.  This is necessary to break in the new cam.

For the first 500 miles, take it easy on the engine.  This is your break-in period.  It is recommended that you spend your first 500 miles varying your speed and RPMs.  Don't take the engine on a long extended road trip during this break-in period.

After 500 miles, change the oil and filter.  This will eliminate any unwanted debris from the new engine.

Make it a point to check the coolant levels a few times to make sure all the hoses are tight and the radiator is full.  Your new engine may run warm for a while as it is breaking in.

It should take the engine between 500 and 1000 miles to fully break in and "loosen up."  Until the engine is broken in, it may not feel as strong as it will eventually get.


This project was finished in the evening on May 4, 2002.  I now have a couple thousand miles on the engine.  The results are as follows:

The engine appears to be very healthy!  Around the local highways here in the Sierra Nevada mountain hills (approximately 2,500 to 4,000 feet) I am able to stay in fifth gear on most of the hills.  I cannot tell if this is because the engine is just fresh or if it is really due to the new head.

The engine does not ping, which it used to do before the rebuild or the Adjustable Fuel Pressure Regulator install.  I am successfully running regular 87 octane fuel in the engine.  

My initial fuel mileage (driving it to work and through town) has been between 12.33 and 13.36 MPG.  On longer highway trips, the MPGs increase to over 15.  Not great, but this is with 33x12.50 tires and very low 4.56 axle gears.